The present invention pertains to the field of transfer printing. More particularly, the subject invention pertains to a process for transfer printing suitable for application to fabrics and other substrates without the use of a polymer coated paper support.
The use of transfer printing to produce signs, lettering, and particularly customized clothing and other textile articles is well known. In the traditional method of transfer printing, a single or multicolor xe2x80x9ctransferxe2x80x9d is prepared by silk screen printing onto an appropriate release substrate. The release substrate may be coated with a polymer adhesive prior to printing the image to be printed, or the print ink itself may contain a polymer adhesive, generally a thermoplastic composition with a melting point below that of the substrate onto which the transfer is to be printed. Alternatively, the printing process may be followed by a second printing wherein adhesive, rather than ink is applied, or the entire transfer may be sprayed with adhesive.
Transfers have also been prepared using pigmented films of carboxylated polyvinylchloride which are cast onto a polyester release sheet following which a thermally activated adhesive is applied. A graphic design is xe2x80x9ckiss-cutxe2x80x9d in reverse through the pigmented carboxylated PVC and adhesive layers but not through the polyester release sheet. After unwanted portions are weeded away, the transfer is applied to the fabric or garment in a heated press, allowed to cool, and the release sheet pulled away, leaving the graphic design adhered to the fabric or garment. This process requires a relatively expensive computer-guided cutting apparatus, and is generally limited to monochrome transfers.
In order to form multi-colored transfers by a conventional process, a separate silk screen must be prepared for each of the primary colors, and if a white area is to be printed, a white pigmented ink must also be applied in a separate printing step. The use of the silk screening process is labor intensive, as the registration of second and subsequent silk screens must closely match that of the first, otherwise an off-register transfer will be produced. Following preparation of the transfer, a computer guided cutting machine accurately cuts around the periphery of the transfer to avoid impregnation of the substrate to be printed with non-functional polymeric material which may detract from the hand and feel of the fabric. Furthermore, the traditional silk screening process is not amenable to the production of transfers of highly detailed subjects, such as those which might be obtained from photographs or computer graphics programs.
Several alternatives to silk screening of transfers are commercially available. In the full color true sublimation transfer process, an impact printer or thermal ribbon printer is used to print a sublimation dye onto a substrate. For full color rendition, a three-head printer must be used or the substrate given multiple passes through a printer after changing color heads. Registration problems may occur during the process, and the resolution is affected by the dot density of the impact or thermal head. The transfer thus created is placed onto the desired article, for example, a T-shirt, cap, or sweatshirt, and heated under modest pressure, during which the dyes coated on the transfer sublime and penetrate the fabric, producing a dyed article. This process is an improvement over silk screening in the sense that it is particularly amenable to computer graphics use, and moreover, the absence of polymer adhesive, particularly in areas surrounding the image, does not alter the hand or feel of fabric.
A related process is the dye sublimation transfer process. In this process, the sublimation dye is first sublimed onto the transfer substrate, and then sublimed a second time onto the desired article. The dye sublimation process affords higher resolution than the full color true sublimation process, however, the colors tend to be less vibrant due to the double sublimation. Higher pressure is also necessary during application, and thus the process is highly suitable for producing customized items such as coffee mugs.
Both the full color true sublimation and dye sublimation processes also suffer from the inability to dye certain substrates. Sublimation dyes are quite effective on polyester fabric or polyester blends, for example polyester/cotton. However cotton or polyester/cotton blends with low polyester content must in general be treated with a solution to enhance the dye penetration. Such processes add to the time and expense of garment preparation. Sublimation processes tend to be relatively expensive, and are generally used only for limited numbers of identical transfers, or where graphics quality is of paramount importance.
Color copiers have been used to produce full color transfers. In this process, a full color original is copied onto a special paper having a fusible polymer coating. The coating must have a fusion temperature higher than that used to set the toner particles from the printer, but less than the article to which they are to be applied. Full color copies of this type are expensive, and some have registration problems, as the same paper passes over multiple toner-apply and heat-set rollers. The use of special polymer coated paper increases the cost, and furthermore, the finished article will have the polymer coating impregnated over the entire corresponding surface unless the transfer is first cut along its periphery. Ink-jet color printers have been used in a manner analogous to color copiers, again using specially coated paper. Once more, the polymer coating is transferred along with the image, across the full width of the paper. However, color ink-jet printers are widely available at modest cost.
It is an object of the present invention to economically produce black and white and full color transfers.
It is a further object of the invention to produce black and white and full color transfers using inexpensive and widely available printing means.
It is a further object of the invention to produce black and white and full color transfers where the cutting of the transfer along the printed periphery is not necessary, and wherein the uncut transfer does not alter the hand and feel of fabric in non-printed areas.
These and other objects are achieved by a transfer printing process wherein a transfer printing ink is directly printed onto a substrate substantially free of fusible or heat-curable polymer with an ink-jet printer, and the resulting transfer is applied to an article under heat and pressure.